Frozen foods compared to their fresh counterparts are usually cheaper, and because of their long expiration date, more convenient. Meat, fish and vegetables can be brought out of the freezer and made ready at any time.
Frozen food has gained a bit of a bad reputation in some circles, but this is due to a generalization. Frozen meals have deservably gained a repuation for being unhealthy. Those meals are packed with preservatives and other additives to make them appear as the dish they are supposed to be. Frozen meals are also mass produced at a factory where the manufacturer will count pennies and cut any corner it can legally cut, as long as it can put a label on the dish without getting sued.
Frozen raw ingredients, on the other hand, are completely legitimate. Many commodities such as peas or berries are harvested once a year in gigantic amounts. What cannot be sold within a few weeks must be preserved or thrown away. Fortunately, the harvested goods can be flash frozen in industral freezers much colder than the ones we have at home. This supercold freezing preserves almost all of the freshness and nutrition of the food.
Berries and fruit
Berries are really only good when they are harvested in their natural harvesting season. The reason so many strawberries are tasteless is because they are grown in greenhouses. This makes berries an ingredient perfect for freezing.
Frozen berries are not interchangeable with their fresh counterparts. When thawed, berries will become soggy and juice will drip off them. This means they cannot be eaten as a snack or used to decorate cakes in a traditional way. What frozen berries are great for is making smoothies, jams, coulis, sauces, cake fillings, milkshakes etc.
Many but all all vegetables are great for freezing. Anything you would boil or roast are pretty much the same whether fresh or frozen. Peas is a great example of this, as their texture will be just as expected when boiled from frozen.
Asparagus, carrots and other vegetables that are often eaten uncooked can lose of its texture and crispness when frozen. If used to make puree or to be mashed, this won't matter much, but there are some foods that are only good when fresh.
Meat and fish
Pretty much all meat and fish are almost just as good whether fresh or frozen. Perhaps some intestines and roe are better not frozen, but all flesh parts of an animal will preserve its texture when thawed.
Since fresh meat and fish get bad so quickly, it's incredibly convenient to have some frozen cuts in the freezer at all times. It's not true that it has to be completely thawed before being cooked, it just needs some more time and perhaps lower temperature.
Bread and pastry
Some bread products are just fine when frozed and bakes at home. Simple baguettes, ciabatta and similar breads can be both delicious and healthy, as they are simple and not full of additives.
Pie crusts, cakes and other pastries with fillings, however, are in almost all cases worse when frozen. The manufactures fill them with all kinds of additives, and will replace natural butter some some seedy oil to save money.